The present invention relates to an ink for ink jet printers which comprises an organic solvent and a pigment dispersed in the organic solvent. More particularly, it relates to an ink for ink jet printers which is improved in dispersion stability of the pigment.
Hitherto, in the field of inks for ink jet printers which comprise an organic solvent and a pigment dispersed therein, the pigment is dispersed using a dispersing agent, and various improvements of printing characteristics and storage stability have been attempted. For example, JP-A-04-161467 and JP-A-04-248879 disclose inks which comprise a silicone-based organic solvent containing a pigment, a resin and a dispersing agent and show attainment of excellent print quality by giving rapid drying characteristics to the inks.
Furthermore, JP-A-05-25417 discloses that an ink jet ink comprising colored resin particles dispersed in a non-polar insulating organic solvent shows no blotting on a recording paper, is excellent in print drying characteristics, causes no clogging of nozzles, and is excellent in scuff resistance.
However, when the silicone-based organic solvent is used, there are no suitable dispersing agents capable of finely dispersing the pigment, and the dispersion particle size of the pigment is large, namely, 0.5-5 μm. Therefore, if the ink is stored for a long period of time, the particles sediment to cause deterioration in print quality. Moreover, in the case of using the colored resin particles, the colored resin particles are ground and dispersed, and, hence, the dispersion particle size is great and the particles sediment to cause deterioration in print quality. In addition, since hydrocarbon solvents are used as the organic solvents, there is a fear in safety for human bodies.
Further, aqueous ink jet inks of pigment type which are generally sold are not satisfactory in water resistance.